The invention relates to a fuel injection valve for internal combustion engines, such as is preferably used for the injection of fuel into a combustion chamber of an auto-ignition internal combustion engine.
Injection systems for the injection of fuel into combustion chambers at high pressure are known from the prior art. Here, fuel is compressed by a high-pressure pump and is temporarily stored in a high-pressure accumulator, a so-called rail. Said high-pressure accumulator provides a feed to one or more fuel injection valves which inject the required fuel into the respective combustion chamber. It is an aim here for exactly the required fuel quantity to be introduced into the combustion chamber as finely atomized and spatially uniform a manner as possible. DE 100 24 702 A1, for example, presents an injection system of said type together with injection valve.
To control the injection, the known fuel injection valves have a nozzle needle which is arranged in longitudinally displaceable fashion in a housing and which, to open and close at least one injection opening, interacts with a nozzle seat. The movement of the nozzle needle is in this case controlled by the pressure in a control chamber, said pressure acting on that face surface of the nozzle needle which faces away from the valve seat. By means of a control valve, the pressure in the control chamber is lowered or raised, which correspondingly changes the closing force on the nozzle needle, such that said nozzle needle, driven by the hydraulic force of the fuel which is at injection pressure and which surrounds the nozzle needle, moves in a longitudinal direction.
The pressure in the control chamber is achieved through the inflow and outflow of pressurized fuel. In the known fuel injection valves, the control chamber is permanently connected to pressurized fuel via an inflow throttle which connects the control chamber to a high-pressure line within the fuel injection valve. To lower the pressure in the control chamber, the control chamber can be connected via an outflow throttle to a low-pressure chamber, wherein the outflow throttle can be opened or closed by means of a control valve. When the outflow throttle is open, pressurized fuel thus flows out of the control chamber into the low-pressure chamber, wherein the pressure in the control chamber, and thus the closing force on the nozzle needle, decrease. This so-called discharge quantity is basically unavoidable owing to the construction principle.
When the control valve is open, fuel flows constantly into the control chamber via the inflow throttle, said fuel expanding in the control chamber and flowing onward into the low-pressure chamber. Said fuel must be compressed by the high-pressure pump in addition to the fuel intended for injection, which reduces the efficiency of the injection system.
To increase the efficiency of the injection system, DE 101 31 617 A1 has disclosed a fuel injection valve in which the fuel pressure in the control chamber is controlled by way of a 3/2 directional valve. Depending on the position of said control valve, fuel either flows from a high-pressure line via an inflow and outflow throttle into the control chamber, or is discharged into a low-pressure chamber. The control by way of a 3/2 directional valve is however cumbersome and expensive. Furthermore, the build-up and dissipation of pressure in the control chamber is relatively slow in the case of this embodiment.